The present invention relates to a defect inspecting method and a defect inspecting system for the inspection of defects existing on a substrate. Here, examples of the substrate are a semiconductor wafer and a mask used for the fabrication of a semiconductor device.
An inspecting apparatus or the like allows the detection of the defects that exist on the substrate such as the semiconductor wafer and the mask. Moreover, the use of an observing apparatus allows observing the details of the defects, collecting the observed images thereof, and analyzing the defects. In the defect inspecting system like this, the observing apparatus is required to be able to promptly execute the positioning as to where the defects detected by the inspecting apparatus exist on the substrate.
Conventionally, as a method of observing the defects on the substrate, there has been known the following method: The substrate as a whole or a portion thereof is inspected in advance so as to confirm whether or not the defects exist. Then, the positions of the defects thus found are stored as their coordinates on the substrate. Next, these stored coordinates are inputted into the observing apparatus through a communications member or a storage medium. Finally, based on the coordinates, the position-alignment is performed so that the defects will enter an observing field-of-view of the observing apparatus, then executing the observation.
At this occasion, if it is the case where the inspecting apparatus and the observing apparatus co-use the same substrate holding mechanism and substrate displacing mechanism and where the substrate remains held by the substrate holding mechanism at the time of transition from the inspection to the observation, simply displacing the observing field-of-view to the specified position-coordinates is enough for the position-alignment toward the observing apparatus. Accordingly, it is quite easy to permit the defects to enter the field-of-view.
In many cases, however, the inspecting apparatus requested to have a high throughput and the observing apparatus requested to have a high observing resolution are different apparatuses. Consequently, the easy position-alignment in the observing apparatus as described above is a difficult task. This requires the sharing of the coordinate system on the substrate by the inspecting apparatus and the observing apparatus through the use of some kind of method. Thus, for example, the following processing is executed: Positions of predetermined plurality of points on the substrate are detected using the inspecting apparatus and the observing apparatus. Then, the coordinate systems characteristic of the respective apparatuses are corrected based on this detection result, thereby causing the substrate coordinate system to be shared by both of the apparatuses.
As the concrete method therefor, there have been known the following methods, for example: A method in which the plurality of points provided along the circumference of the substrate and becoming a criterion of the positioning are constrained mechanically by the substrate holding mechanism, or a method in which an image of a predetermined pattern existing beforehand on the substrate is detected and the coordinate systems are corrected based on the position of this pattern.
JP-A-3-156947 has disclosed one example of the methods in which there is used the coordinate system that is common to a plurality of apparatuses including the inspecting apparatus and the observing apparatus.
In the above-described prior art method of mechanically constraining the points on the substrate, there exists a problem in the mechanical position reproducibility, i.e., the dimension accuracy. For example, it is difficult to implement the high-accuracy position-alignment at a level of micrometers.
Also, concerning the above-described method of correcting the coordinate systems in accordance with the detected pattern position, the method is inapplicable to, for example, the substrate before the pattern""s formation of course. Moreover, when, for example, the inspecting apparatus is an optical type and the observing apparatus is an electron-beam type, i.e., the pattern detecting methods and the pattern detecting accuracies are different between both of the apparatuses, there exists the case where it is impossible to detect the same pattern in common to the apparatuses. Accordingly, the method is inapplicable to this case.
For example, when the substrate is covered with a transparent oxide-film and a pattern existing under the oxide-film is used for the position-alignment of the optical type inspecting apparatus, it is difficult to detect the pattern with the use of the electron-beam type observing apparatus.
JP-A-11-167893 has disclosed one example of the methods of detecting foreign substances in the case where the detecting methods are different between the inspecting apparatus and the observing apparatus. In this example, using both the coordinate values of the foreign substances on the substrate and the coordinate values thereof on the stage, it is intended to implement the sharing of the coordinate system between the inspecting apparatus and the observing apparatus. This makes it easier for the observing apparatus to find out the foreign substances that have been detected by the inspecting apparatus. Furthermore, the detected foreign substances are automatically selected depending on the characteristics such as the size, thereby enhancing the reliability of a correcting formula for the sharing of the coordinate system.
However, even if the inspecting apparatus and the observing apparatus employ the detecting methods similar to each other, when, for example, trying to observe into what form the defects detected at the time of the inspection have changed after the inspected substrate had been subjected to several processing steps, the pattern turns out to exist under a film formed at the processing steps. Consequently, it becomes impossible to detect the same pattern.
It is an object of the present invention to implement efficiency-heightening and time-shortening of a defect observing operation, a defect image collecting operation, and a defect analyzing operation.
Also, it is another object of the present invention to allow a short-time and high-efficiency defect observation to be executed when the inspecting method and the observing method differ from each other.
Conventionally, when the substrate before the pattern""s formation is inspected and observed, or when the inspecting apparatus and the observing apparatus are unable to detect the same pattern, it was difficult to cause the defects detected by the inspecting apparatus to enter the observing field-of-view of the observing apparatus with a high-accuracy. As the countermeasures against this, for example, the following attempts have been made: The defects are searched for in such a manner as to reduce the observing magnification of the observing apparatus to a lower magnification, or the operator searches for the defects with the high magnification left unchanged. In such operations, however, there existed a problem of taking so much labor and time.
Also, conventionally, when the optical conditions employed differ between the inspecting method and the observing method, it was not necessarily easy for the observing apparatus to observe the defect candidates that have been detected by the inspecting apparatus. As a result, there existed a problem of spending wasted time in changing the observing conditions or making a search around where the defects exist.
When the observing apparatus performs the observation, the collection of the observed images, and the defect analysis toward the defects detected by the inspecting apparatus, the present invention executes the position-alignment toward the detected defects with a high-accuracy. This allows the images to be detected at a time with a higher magnification, thereby implementing the efficiency-heightening and the time-shortening of the defect observing operation, the defect image collecting operation, and the defect analyzing operation.
Also, when the inspecting method and the observing method differ from each other, the present invention excludes, from the inspection result, a defect candidate the detection of which is impossible by the observing method, thereby making it possible to execute the short-time and high-efficiency defect observation.
According to the embodiments of the present invention, in addition to in-substrate coordinate system plurality of defects"" position-coordinates detected and extracted by the inspecting apparatus, attribute of the defects is outputted. Here, examples of the attribute are as follows: The dimension, the type, the scattered light amount, local variation in the luminance, the profile configuration, and so on.
Next, based on the defects"" position-coordinates and the defects"" attribute inputted from the inspecting apparatus, a plurality of defects that are judged to be easily detectable by the observing apparatus are selected. Then, based on the selected defects"" position-coordinates, the image detection is performed by the observing apparatus so as to find out the defects. Moreover, based on the defects"" positions within the image, in-substrate coordinate system defects"" position-coordinates defined on the observing apparatus side are calculated. Since, essentially, the substrate coordinate system is fixed onto the substrate, the in-substrate coordinate system represented defects"" position-coordinates defined on the inspecting apparatus side and inputted from the inspecting apparatus should completely coincide with the in-substrate coordinate system defects"" position-coordinates defined on the observing apparatus side.
As described earlier, however, the approximate position-alignment has been made where the mechanical position-alignment mechanism using, for example, the substrate circumference or the like makes it unhopeful to expect the high-accuracy. Consequently, it is usual at this point in time that the substrate coordinate system defined on the observing apparatus side differs from the substrate coordinate system defined on the inspecting apparatus side.
Accordingly, based on the in-substrate coordinate system defects"" position-coordinates defined on the observing apparatus side and the in-substrate coordinate system defects"" position-coordinates defined on the inspecting apparatus side and inputted from the inspecting apparatus, a coordinate transformation from the substrate coordinate system defined by the inspecting apparatus to the substrate coordinate system defined by the observing apparatus is derived with respect to the defects selected by the inspecting apparatus.
In accordance with this coordinate transformation, the defects"" position-coordinates inputted from the inspecting apparatus are transformed into the position-coordinates in the substrate coordinate system defined by the observing apparatus. Hereinafter, the defect observation and the like will be executed based on these transformed position-coordinates.
Also, information on this coordinate transformation is saved and stored in a database with a set of the inspecting apparatus and the observing apparatus regarded as the unit. When executing the observation at the next opportunity, the position-alignment is performed first, using the information on this coordinate transformation. If a new coordinate transformation is derived by the above-described method, the above-described information on the coordinate transformation is updated.
In the present invention, the defects that actually exist on the substrate and are easily detectable in common by the observing apparatus are selected, then being used as the criterion of the substrate position-alignment. Consequently, even when there exists no pattern for the position-alignment, or even when, if any, the pattern is unable to be used in common to the inspecting apparatus and the observing apparatus, it becomes possible for the observing apparatus to execute the position-alignment toward the defects"" positions with a high-accuracy.
Also, in the present invention, based on the defects"" position-coordinates and the defects"" attribute, only the defects that are judged to be easily detectable by the observing apparatus are observed. This makes the efficient defect observation possible.
Furthermore, the information on the coordinate transformation between the inspecting apparatus and the observing apparatus is stored in the database for use, or the information is updated. This makes it possible to always execute the defect observation based on a more precise positioning.
As described earlier, when the observing apparatus performs the observation, the collection of the observed images, and the defect analysis toward the defects detected by the inspecting apparatus, the present invention executes the position-alignment toward the detected defects with a high-accuracy. This allows the images to be detected at a time with a higher magnification, thereby making it possible to implement the efficiency-heightening and the time-shortening of the defect observing operation, the defect image collecting operation, and the defect analyzing operation.
Also, when the inspecting method and the observing method differ from each other, the present invention excludes, from the inspection result, a defect candidate the detection of which is impossible by the observing method, thereby making it possible to provide the method of executing the short-time and high-efficiency defect observation.